Meeting Abstract
Multiple, long limbs of arthropods can permit larger workspaces to find secure footholds and result in greater step lengths for rapid locomotion, if geometry does not constrain their trajectories. We defined a limb’s workspace as a 3D volume that represents all possible footholds relative to the animal’s body. We captured the morphology of the mid and hind limbs of cockroaches, Blaberus discoidalis, using photogrammetry and optical measures of joint range of motion. We modelled limbs as serial kinematic chains. The mid and hind workspace volumes extended the body volume space by 220 and 510 %, respectively, with a 16% intersection among leg workspace volumes. We parsed workspaces by decomposing them into step lines, segments of possible footholds parallel to the body axis that represent possible step lengths. We examined the potential trade-off of a secure foothold using a follow-the-leader (FTL) gait versus the maximum possible step length for high speed. A FTL gait requires that the posterior leg step within a possible secure foothold of the next anterior ipsilateral leg. For a fixed body pitch, an alternating tripod gait on level ground requires mid and hind step lines to be coplanar. For a follow-the-leader gait, step lines must additionally be collinear and possess a region of overlap. Surprisingly, when we searched for the longest collinear mid/hind step line pairs (top 5% at 15.1mm±6.7mm S.D.), we found an average overlap of 8.5mm. Moreover, the maximum collinear step length (25.6mm) was consistent with the maximum step length measured at maximum speed running (25 mm). Our model is a first step toward the creation of a structure-function design space for arthropod legs to reveal general design principles.
